TY - JOUR T1 - Characteristics of the Liver Microsomal Drug-Metabolizing Enzyme System of Newborn Rats JF - Molecular Pharmacology JO - Mol Pharmacol SP - 1092 LP - 1104 VL - 13 IS - 6 AU - MICHAEL M. IBA AU - LESTER F. SOYKA AU - MARTIN P. SCHULMAN Y1 - 1977/11/01 UR - http://molpharm.aspetjournals.org/content/13/6/1092.abstract N2 - Sodium dithionite-reduced hepatic microsomes from neonatal (5-7-day-old) rats displayed (a) an absorption maximum at 452 nm in the presence of carbon monoxide and (b) an equilibrium for the ethyl isocyanide-induced absorption peaks at 430 and 455 nm at pH 7.9. These preparations elicited little or no spectral change with ethylmorphine but elicited the type R-I spectral change with other type I substrates. Carbon monoxide formation in the presence of NADPH and the rate of conversion of cytochrome P-450 to cytochrome P-420 by mersalyl (sodium [(3-hydroxymercuri-2-methoxypropyl)-carbamoyl]phenoxyacetate) were greater in microsomes from neonates than in those from adults. In the presence of NADPH, lipid peroxidatic activity was high, ethylmorphine N-demethylation was low, and aniline hydroxylation was the same in microsomes from neonates compared with the same activities in microsomes from adults. In the presence of NADH, ethylmorphine N-demethylase activities in both the adult and neonatal preparations were identical, but more cytochrome P-450 was reducible by this nucleotide in the latter preparation. These observations demonstrate that the drug-metabolizing system of the neonate differs from that of the adult. ER -